Spacer fluid compositions, methods, and systems for aqueous based drilling mud removal

ABSTRACT

Spacer fluids include an emulsion, a surfactant package, and at least one additive that modifies the rheology of the spacer fluid, the density of the spacer fluid, or both. The emulsion may include an aqueous external phase and a hydrocarbon-based internal phase. The surfactant package may include one or more surfactants. The surfactant package may also include a surfactant having the general structure R—(OCH2CH2)9—OH, where R is a hydrocarbyl having 12 carbon atoms, 13 carbon atoms, or 14 carbon atoms. The spacer fluid may contain at least 4.25 pounds of R—(OCH2CH2)9—OH per barrel of the spacer fluid.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationSer. No. 62/454,189 filed Feb. 3, 2017, and to U.S. Provisional PatentApplication Ser. No. 62/454,192 filed Feb. 3, 2017, both of which areincorporated by reference in their entirety.

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to spacer fluidcompositions, methods, and systems used for removing aqueous baseddrilling muds from wellbores and subterranean hydrocarbon bearingformations.

BACKGROUND

During drilling operations, drilling fluids, which may also be referredto as drilling muds, are circulated through the wellbore to cool thedrill bit and maintain the wellbore. Also during drilling operations, acement slurry may be introduced into the wellbore to secure thestructure of the wellbore. Drilling muds may be either aqueous orhydrocarbon-based and vary in composition.

Under some conditions, the presence of drilling muds in the wellborenegatively affects the performance of the cement slurry. In theseconditions, it is sometimes desirable to pass a spacer fluid through thewellbore.

SUMMARY

Wellbores are commonly cemented by filling an annulus between thetubular and the wellbore wall with a cement slurry. Prior to beingcemented, the wellbore may be filled with a drilling fluid, also knownas a drilling mud. The presence of the drilling mud may negativelyaffect the performance of the cement slurry. A spacer fluid may be addedinto the wellbore to remove the drilling fluid from the wellbore priorto the addition of the cement slurry. Accordingly, there is a need forspacer fluids, methods, and systems for the displacement of aqueousmuds. The present embodiments address this need by providing spacerfluids, methods of using spacer fluids to displace aqueous muds, andwellbore fluid systems comprising a spacer fluid and an aqueous muddisposed in a wellbore.

The presently disclosed spacer fluids typically include at least anemulsion, a surfactant package, and at least one additive that modifiesthe rheology of the spacer fluid, the density of the spacer fluid, orboth. In some embodiments, one role of the surfactant package in thespacer fluids is to improve mud removal efficiency of the spacer fluid.The spacer fluids according to embodiments include a surfactant packagethat includes an ethoxylated alcohol surfactant having the formulaR—(OCH₂CH₂)₉—OH, where R is a hydrocarbyl having from 12 to 14 carbonatoms. The ethoxylated alcohol surfactant may improve mud removalefficiency of the spacer fluid.

In one embodiment, a spacer fluid comprises an emulsion, a surfactantpackage, and at least one additive that modifies the rheology of thespacer fluid, the density of the spacer fluid, or both. The emulsion maycomprise an aqueous external phase and a hydrocarbon-based internalphase. The surfactant package may comprise one or more surfactants. Thesurfactant package may also comprise a surfactant having the generalchemical structure R—(OCH₂CH₂)₉—OH. In one embodiment, R is ahydrocarbyl having 12 carbon atoms and the surfactant R—(OCH₂CH₂)₉—OH ispresent in a concentration of at least 4.25 pounds per barrel of spacerfluid (where 1 pound equals 0.454 kilograms and 1 barrel is equivalentto 159 liters). In other embodiments, R may be a hydrocarbyl having 13or 14 carbon atoms.

In another embodiment, a method of removing aqueous muds from a wellborecomprises adding a spacer fluid to a wellbore comprising an aqueous mud,passing the spacer fluid through the wellbore, and at least a portion ofthe aqueous mud exits the wellbore through a conduit defined by anexterior wall of the tubular and a wall of the wellbore. The spacerfluid may comprise an emulsion, a surfactant package, and at least oneadditive that modifies the rheology of the spacer fluid, the density ofthe spacer fluid, or both.

In yet another embodiment, a wellbore fluid system comprises an aqueousmud and a spacer fluid both disposed in a wellbore. The aqueous mud andthe spacer fluid may both have a density and a yield point measured byAmerican Petroleum Institute Recommended Practice 13B-1. The spacerfluid may comprise an emulsion, a surfactant package, and at least oneadditive that modifies the rheology of the spacer fluid, the density ofthe spacer fluid, or both. The density of the spacer fluid is 5% to 20%greater than the density of the aqueous mud and the difference of theyield point of the aqueous mud and the yield point of the spacer fluidmay be less than or equal to 15 lbs/100 ft².

Additional features and advantages of the described embodiments will beset forth in the detailed description which follows, and in part will bereadily apparent to those skilled in the art from that description orrecognized by practicing the described embodiments, including thedetailed description which follows as well as the claims.

DETAILED DESCRIPTION

Embodiments of the present application are directed to a spacer fluidcomposition, in particular, a spacer fluid composition that isrheologically compatible with an aqueous drilling mud. The spacer fluidmay comprise an emulsion, a surfactant package in the emulsion, and atleast one additive. The emulsion may comprise an aqueous external phaseand a hydrocarbon-based internal phase. The surfactant package maycomprise one or more surfactants, which may comprise an ethoxylatedalcohol surfactant according to Formula (I):R—(OC₂H₄)₉—OH  (I)where R is a hydrocarbyl having from 12 to 14 carbon atoms. A surfactantof Formula (I) of the surfactant package may have ahydrophilic-lipophilic balance (HLB) from 11 to 15. The one or moreadditives may modify the viscosity of the spacer fluid, the density ofthe spacer fluid, or both.

Other embodiments of the present application relate to methods forremoving aqueous based drilling muds from a wellbore. The method maycomprise passing a spacer fluid through the wellbore. The wellbore maycomprise an annulus, an exterior, an outlet disposed at the surface ofthe wellbore, and at least one aqueous mud. The spacer fluid maycomprise an emulsion, a surfactant package in the emulsion, and at leastone additive. The emulsion may comprise an aqueous external phase and ahydrocarbon-based internal phase. The surfactant package may comprise anethoxylated alcohol surfactant according to formula (I) where R is ahydrocarbyl having from 12 to 14 carbon atoms. The surfactant packagemay have an HLB value from 11 to 15. The spacer fluid additive oradditives may modify the viscosity of the spacer fluid, the density ofthe spacer fluid, or both. The passing spacer fluid may be directedthrough the annulus and out the outlet of the wellbore. The spacer fluidmay then direct the aqueous mud in the wellbore to flow through theannulus and out the outlet of the wellbore.

Still other embodiments of the present application relate to a wellborefluid system comprising an aqueous mud and a spacer fluid both disposedin a wellbore. The spacer fluid may comprise an emulsion, a surfactantpackage comprising one or more surfactants in the emulsion, and at leastone additive. The emulsion may comprise an aqueous external phase and ahydrocarbon-based internal phase. The surfactant package may comprise anethoxylated alcohol surfactant according to formula (I) where R is ahydrocarbyl having from 12 to 14 carbon atoms. The ethoxylated alcoholsurfactant may have an HLB value from 11 to 15. The one or moreadditives may modify the viscosity of the spacer fluid, the density ofthe spacer fluid, or both. In some embodiments of the wellbore fluidsystem, the density of the spacer fluid is 5% to 20% greater than thedensity of the aqueous mud. In some embodiments of the wellbore fluidsystem, the difference between the yield point of the aqueous mud andthe yield point of the spacer fluid may be less than 15 pounds perhundred square feet (lbs/100 ft²).

A wellbore is a hole that extends from the surface to a location belowthe surface. The wellbore can permit access as a pathway between thesurface and a hydrocarbon-bearing formation. The wellbore, defined andbound along its operative length by a wellbore wall, extends from aproximate end at the surface, through the subsurface, and into thehydrocarbon-bearing formation, where it terminates at a distal wellboreface. The wellbore forms a pathway capable of permitting both fluid andapparatus to traverse between the surface and the hydrocarbon-bearingformation.

Besides defining the void volume of the wellbore, the wellbore wall alsoacts as the interface through which fluid can transition between theinterior of the wellbore and the formations through which the wellboretraverses. The wellbore wall can be unlined (that is, bare rock orformation) to permit such interaction with the formation or lined (thatis, with casing, tubing, production liner or cement) so as to not permitsuch interactions.

The wellbore usually contains at least a portion of at least one fluidconduit that links the interior of the wellbore to the surface. Examplesof such fluid conduits include casing, liners, pipes, tubes, coiledtubing and mechanical structures with interior voids. A fluid conduitconnected to the surface is capable of permitting regulated fluid flowand access between equipment on the surface and the interior of thewellbore. Example equipment connected at the surface to the fluidconduit includes pipelines, tanks, pumps, compressors and flares. Thefluid conduit is sometimes large enough to permit introduction andremoval of mechanical devices, including tools, drill strings, sensorsand instruments, into and out of the interior of the wellbore.

The fluid conduit made from a tubular usually has at least two openings(typically on opposing ends) with an enclosing surface having aninterior and exterior surface. The interior surface acts to define thebounds of the fluid conduit. Examples of tubulars and portions oftubulars used in the wellbore as fluid conduits or for making orextending fluid conduits include casing, production liners, coiledtubing, pipe segments and pipe strings. An assembly of several smallertubulars connected to one another, such as joined pipe segments orcasing, can form a tubular that acts as a fluid conduit.

When positioning a tubular or a portion of tubular in the wellbore, thevolume between the exterior surfaces of the fluid conduit or tubularportion and the wellbore wall of the wellbore forms and defines awellbore annulus. The wellbore annulus has a volume in between theexternal surface of the tubular or fluid conduit and the wellbore wall.

During a drilling operation on a wellbore, drilling fluid, also known asdrilling mud, fills the interior of the wellbore as the wellbore fluid.Some drilling muds are petroleum-based compositions and some arewater-based compositions. Drilling muds that are water-basedcompositions are also known as aqueous muds. Aqueous muds usuallycomprise from 30 to 351 pounds of water per barrel of drilling mud,where a barrel is defined as 42 gallons or 159 liters. The remainder ofaqueous muds may comprise minerals, additives that modify viscosity ordensity, weighting agents, salts, emulsifiers, or other materials.

During drilling operations on a wellbore, wellbore fluid circulatesbetween the surface and the wellbore interior through fluid conduits.Wellbore fluid also circulates around the interior of the wellbore. Theintroduction of drilling fluid into the wellbore through a first fluidconduit at pressure induces the motivation for the fluid flow in thewellbore fluid. Displacing wellbore fluid through a second fluid conduitconnected to the surface induces wellbore fluid circulation from thefirst fluid conduit to the second fluid conduit in the interior of thewellbore. The expected amount of wellbore fluid displaced and returnedto the surface through the second fluid conduit is equivalent to theamount introduced into the wellbore through the first fluid conduit.Parts of the wellbore that are fluidly isolated do not supportcirculation.

Cementing is one of the most important operations in both drilling andcompletion of the wellbore. Primary cementing occurs at least once tosecure a portion of the fluid conduit between the wellbore interior andthe surface to the wellbore wall of the wellbore.

A variety of water-based cements slurries are available for primarycementing operations. Primary cements typically contain calcium,aluminum, silicon, oxygen, iron and sulfur compounds that react, set andharden upon the addition of water. The water used with the cement slurrycan be fresh water or salt water and depend on the formation of thecement slurry and its tolerance to salts and free ions. Suitablewater-based cements include Portland cements, pozzolana cements, gypsumcements, high alumina content cements, slag cements, silica cements,high alkalinity cements, latex and resin-based cements.

Primary cementing forms a protective solid sheath around the exteriorsurface of the introduced fluid conduit by positioning cement slurry inthe wellbore annulus. Upon positioning the fluid conduit in a desirablelocation in the wellbore, introducing cement slurry into the wellborefills at least a portion if not all of the wellbore annulus. When thecement slurry cures, the cement physically and chemically bonds withboth the exterior surface of the fluid conduit and the wellbore wall,coupling the two. In addition, the solid cement provides a physicalbarrier that prohibits gases and liquids from migrating from one side ofthe solid cement to the other via the wellbore annulus. This fluidisolation does not permit fluid migration uphole of the solid cementthrough the wellbore annulus.

Displacing wellbore fluid for primary cementing operations is similar toestablishing circulation in the wellbore fluid with a drilling mud. Anamount of cement slurry introduced into the wellbore through a firstfluid conduit induces fluid flow in the wellbore and displaces anequivalent amount of wellbore fluid to the surface through a secondfluid conduit. In such an instance, the wellbore fluid includes aportion of the wellbore fluid previously contained in the wellborebefore cement introduction as well as the amount of the introducedcement slurry.

Direct contact of the cement slurry with the drilling mud can result indetrimental fluid interactions that can jeopardize not only cementingoperations but also the integrity of the wellbore. The intermingling ofincompatible fluids can create emulsions between the fluids. Theemulsions, which resist fluid movement upon the application of force,raise the viscosity profile of the wellbore fluid. Increasing pumpinghead pressure to maintain a constant fluid circulation rate in thewellbore can result in damaging the formation downhole as wellbore fluidpressure exceeds the fracture gradient of the formation.

Besides detrimentally affecting the viscosity profile, when solids andwater from the cement slurry transfer into the drilling mud duringemulsification, the properties of the drilling mud are detrimentallyaffected. Dilution, chemical interaction, breaking of a water-in-oilemulsion and flocculation of suspended additives out of the oil phasecan also occur.

Cement slurry properties can also suffer from contamination by thedrilling mud. Flocculation of weighting agents and macromolecules cancause the cement to have reduced compressive strength. The diffusion ofionic species from the drilling mud can cause premature setting of thecement slurry. The ramifications of early cement hardening includeequipment damage, time delay, wellbore damage and possible loss of theentire tubular string. Contamination of the cement slurry with drillingmud results in higher slurry viscosity and higher fluid losses from thehardening slurry.

Without being bound by theory, it is believed that the spacer fluidspresently disclosed may have a beneficial effect with respect to one ormore of the problems with spacer cementing processes described. Thespacer fluids of the present disclosure have a greater aqueous mudremoval efficiency than that of previously known spacer fluids includingsurfactant packages that do not contain the ethoxylated alcoholsurfactant according to Formula (I). Spacer fluids with greater mudremoval efficiency can limit, decrease, or prevent the aqueous mud frominteracting with the cement slurry and adversely affecting the cementingprocess.

As previously described in the present description, the spacer fluid maycomprise one or more of an emulsion, a surfactant package, and at leastone additive that modifies the rheology of the spacer fluid, the densityof the spacer fluid, or both. It should be understood that whileembodiments of spacer fluids presently described include thesecomponents, other components may be included in a spacer fluid forvarious functional reasons, and it is contemplated that additionalcomponents may be included in the spacer fluids presently described. Asused in this disclosure, a “surfactant package” refers to the group ofone or more surfactant species which are included in the spacer fluid.For example, a surfactant package may include a single chemical species,or may alternatively include more than one chemical species.

Spacer fluids have the greatest mud removal efficiency in a wellborewhen they have similar rheological properties to the drilling mud beingcirculated in the wellbore and the density of the spacer fluid is 5% to20% greater than the density of the drilling mud. As will be describedsubsequently in greater detail, fluids are considered to have similarrheological properties when they have similar yield points (YPs) andplastic viscosities (PVs). Mud removal efficiency describes the extentto which a given spacer fluid is capable of displacing a given drillingmud. Mud removal efficiency can be quantitatively measured with a gridtest.

The rheology of spacer fluids of the present disclosure and aqueousdrilling muds can be described by the Bingham plastic model. The Binghamplastic model assumes a linear relationship between the shear stress andthe shear rate of a fluid. Fluids that exhibit Bingham plastic behaviordo not flow until the shear stress exceeds the yield point (YP) of thefluid. Once the yield point is reached, changes in shear stress andshear rate are proportional. The constant of this proportionality isknown as the plastic viscosity (PV).

The yield point and density of a drilling mud are related to the abilityof the drilling mud to remove formation cuttings from the wellbore.Spacer fluids of the present disclosure are formulated to be compatiblewith the rheology and density of such drilling muds. The rheologicalbehavior of a drilling mud or spacer fluid can be determined bymeasuring the shear stress on the fluid at different shear rates. Thismay be accomplished by measuring the shear stress on the fluid using aFANN Model 35 viscometer operated at 0.05 Hz (3 RPM), 0.1 Hz (6 RPM),1.67 Hz (100 RPM), 3.33 Hz (200 RPM), 5 Hz (300 RPM), and 10 Hz (600RPM).

The plastic viscosity of a fluid is related to the resistance of thatfluid to flow due to mechanical interactions between the components ofthe fluid. The plastic viscosity of a fluid may be calculated bymeasuring the shear stress of the fluid using a viscometer at shearrates of 5 Hz (300 RPM) and 10 Hz (600 RPM) and subtracting the 5 Hzviscosity from the 10 Hz viscosity as shown in Eq. (1).PV=(viscosity at 10 Hz)−(viscosity at 5 Hz)  Eq. (1)High shear rates are chosen for this calculation because the viscosityof Bingham plastic fluids exhibit more linear behavior at higher shearrates.

The yield point (YP) represents the minimum shear stress required tomake a fluid flow. If a fluid is subjected to a shear stress less thanthe fluid's yield point, then the fluid will behave as a rigid body. Ifa fluid is subjected to a shear stress at or greater than the fluid'syield point, then the fluid will flow. The yield point is representativeof a fluid's carrying capacity. A fluid with a greater yield point willbe able to carry more mass. A drilling mud with a greater yield pointcan carry a greater mass of formation cuttings. A spacer fluid with agreater yield point can displace a greater mass of drilling mud. Theyield point of a drilling mud can be tailored for specific situations orspecific types of formation cutting removal by altering the compositionof the mud. Spacer fluids can be designed to have yield points similarto the drilling mud by including additives that modify the rheology ofthe spacer fluid.

The yield point of a fluid is determined by extrapolating the Binghamplastic rheology model to a shear rate of zero according to AmericanPetroleum Institute Recommended Practice 13B-1, incorporated byreference into this disclosure in its entirety. The yield point of afluid can be calculated from rheological data and the plastic viscosityaccording to Eq. (2).YP=(viscosity at 5 Hz)−PV  Eq. (2)The yield point is expressed as a force per area, such as pounds offorce per one hundred square feet (lbf/100 ft²) or newtons per squaremeter (N/m²). One pound of force per one hundred square feet is equal toabout 4788 newtons per square meter (1 lbf/100 ft²=4788 N/m²).

In some embodiments, the spacer fluid may have a yield point from 10lbf/100 ft² to 50 lbf/100 ft². In other embodiments, the spacer fluidmay have a yield point from 10 lbf/100 ft² to 40 lbf/100 ft², from 10lbf/100 ft² to 30 lbf/100 ft², from 10 lbf/100 ft² to 25 lbf/100 ft²,from 10 lbf/100 ft² to 20 lbf/100 ft², from 10 lbf/100 ft² to 15 lbf/100ft², from 15 lbf/100 ft² to 50 lbf/100 ft², from 15 lbf/100 ft² to 40lbf/100 ft², from 15 lbf/100 ft² to 30 lbf/100 ft², from 15 lbf/100 ft²to 25 lbf/100 ft², from 15 lbf/100 ft² to 20 lbf/100 ft², from 15lbf/100 ft² to 18 lbf/100 ft², from 18 lbf/100 ft² to 25 lbf/100 ft², orfrom 18 lbf/100 ft² to 20 lbf/100 ft².

In some embodiments, the spacer fluid may have a density from 62.5pounds per cubic feet (pcf) to 160 pcf (where 1 pcf=16.0185 kg/m³). Inother embodiments, the spacer fluid may have a density from 62.5 pcf to140 pcf; from 62.5 pcf to 120 pcf; from 62.5 pcf to 100 pcf; from 65.0pcf to 160 pcf; from 65.0 pcf to 140 pcf; from 65.0 pcf to 120.0 pcf;from 65.0 pcf to 100.0 pcf; from 68.5 pcf to 160 pcf; from 68.5 pcf to140 pcf; from 68.5 pcf to 120.0 pcf; from 68.5 pcf to 100.0 pcf; from72.0 pcf to 160 pcf; from 72.0 pcf to 140 pcf; from 72.0 pcf to 120.0pcf; from 72.0 pcf to 100.0 pcf; from 75.0 pcf to 160 pcf; from 75.0 pcfto 140 pcf; from 75.0 pcf to 120.0 pcf; or from 75.0 pcf to 100.0 pcf.

The spacer fluids of the present disclosure comprise an emulsion havingan aqueous external phase and a hydrocarbon-based internal phase. Theaqueous external phase may by any suitable fluid such as water or asolution containing both water and one or more organic or inorganiccompounds dissolved in the water or otherwise completely miscible withthe water. The aqueous external phase may comprise purified water,mineral water, brine water, fresh water, distilled water, sea water,salt water, other aqueous solutions, or combinations thereof. Inembodiments, the aqueous external phase may comprise brine, includingnatural and synthetic brine. The aqueous external phase may includewater containing water-soluble organic compounds, such as alcohols,organic acids, amines, aldehydes, ketones, esters, or other polarorganic compounds, such as alcohols, organic acids, amines, aldehydes,ketones, esters, or other polar organic compounds or salts dissolved inthe water.

The internal phase may be any suitable fluid such as oil or a solutioncontaining both oil and one or more organic or inorganic compoundsdissolved in the oil or otherwise completely miscible with the oil. Theinternal phase may comprise safra oil, diesel, mineral oil, paraffinoil, ben oil, marula oil, castor oil, palm oil, copra oil, jojoba oil,tung oil, other oils naturally derived from plants or animals, orcombinations thereof. Without being limited by theory, it is believedthat the internal phase may be statistically evenly dispersed within theexternal phase.

In one or more embodiments the spacer fluid comprises from 140 pounds to315 pounds of aqueous external phase per barrel of spacer fluid. Inother embodiments, the spacer fluid comprises from 160 pounds to 300pounds, 180 pounds to 300 pounds, 200 pounds to 300 pounds, 220 poundsto 300 pounds, 140 pounds to 280 pounds, 160 pounds to 280 pounds, 180pounds to 280 pounds, 200 pounds to 280 pounds, or 220 pounds to 280pounds of aqueous external phase per barrel of spacer fluid.

In one or more embodiments the spacer fluid comprises from 5 pounds to60 pounds of hydrocarbon-based internal phase per barrel of spacerfluid. In other embodiments, the spacer fluid comprises from 10 poundsto 50 pounds, 15 pounds to 40 pounds, 15 pounds to 30 pounds, or 20pounds to 30 pounds of hydrocarbon-based internal phase per barrel ofspacer fluid.

The spacer fluids of the present disclosure further comprise asurfactant package comprising one or more surfactants. The surfactantpackage may comprise an ethoxylated alcohol surfactant according toFormula (I):R—(OC₂H₄)₉—OH  (I)where R is a hydrocarbyl having from 12 to 14 carbon atoms. In someembodiments, R can be a saturated, unsaturated, linear, branched, oraromatic hydrocarbyl such as, by way of non-limiting examples, —C₁₂H₂₅or —(CH₂)₅CH(CH₃)CH₂CH₂CH(CH₃)₂. In embodiments, R may be a saturated orunsaturated hydrocarbyl, such as a saturated alkyl (—C_(y)H_(2y+1) wherey is from 12 to 14), unsaturated alkyl (—C_(y)H_((2y−2z−4w+1)) where yis from 12 to 14, z is the number of double bonds in R, and w is thenumber of triple bonds in R), alkenyl (—CH═CHC_(y)H_((2y−2z−4w+1)) wherey is from 10 to 12, z is a number of additional double bonds in R, and wis the number of triple bonds in R), alkynyl (—C≡CC_(y)H_((2y−2z−4w+1))where y is from 10 to 12, z is the number of double bonds in R, and w isthe number of additional triple bonds in R). Each of the generalformulas for saturated alkyl, unsaturated alkyl, alkenyl, and alkynylincludes both linear groups and branched groups having 1, 2, 3, 4, 5, orgreater than 5 branches at individual carbon atoms. Examples of linearhydrocarbyl groups include, without limitation, linear alkyls of formula—(CH₂)_(y)CH₃ where y is from 11 to 13 and linear alkenyls of formula—CH═(CH₂)_(y)CH₃ where y is an integer from 10 to 12. Specific examplesof linear alkyls include n-decyl, n-undecyl, and n-dodecyl. Inembodiments, R can be a saturated, unsaturated, linear, branched, oraromatic hydrocarbyl having from 12 to 13 carbon atoms, from 13 to 14carbon atoms, exactly 12 carbon atoms, exactly 13 carbon atoms, orexactly 14 carbon atoms.

In one embodiment the spacer fluid may comprise from 0.40 pounds to 21pounds of surfactant package per barrel of spacer fluid. In otherembodiments, the spacer fluid may comprise from 1 pound to 18 pounds,from 3 pounds to 15 pounds, from 4 pounds to 12 pounds, or from 5 poundsto 10 pounds of surfactant package per barrel of spacer fluid.

The ethoxylated alcohol surfactant may be the condensation product of anethoxylation reaction of a fatty alcohol. The fatty alcohol is analcohol having a formula R—OH, where R is a saturated or unsaturated,linear, or branched hydrocarbyl. In some embodiments, R has from 12 to14 carbon atoms. In other embodiments, R may have exactly 12 carbonatoms, exactly 13 carbon atoms, or exactly 14 carbon atoms. In one ormore embodiments, R may be a saturated linear hydrocarbyl. In otherembodiments, R may be an unsaturated linear hydrocarbyl. Still, in otherembodiments, R is a branched hydrocarbyl.

In some embodiments, the fatty alcohol may be a naturally occurringfatty alcohol, such as a fatty alcohol obtained from natural sourcessuch as animal products or vegetable oils. Non-limiting examples ofnaturally occurring fatty alcohols include, but are not limited to,capric alcohol, decyl alcohol, lauryl alcohol, myristyl alcohol, cetylalcohol, stearyl alcohol, palmitoeyl alcohol, heptadecanol, nonadecylalcohol, arachidyl alcohol, other naturally-occuring fatty alcohols,other synthetic alcohols, or combinations thereof.

In some embodiments, the fatty alcohol may be a synthetic fatty alcoholprepared from a synthesis reaction using one or more petroleum basedprecursors. For example, one embodiment may use the oligomerization ofethylene to produce a fatty alcohol having a formula R—OH where R is asaturated or unsaturated, linear, or branched hydrocarbyl. In someembodiments, R has from 12 to 14 carbon atoms. In other embodiments, Rmay have exactly 12 carbon atoms, exactly 13 carbon atoms, or exactly 14carbon atoms.

The ethoxylation of a fatty alcohol, R—OH to form the ethoxylatedalcohol surfactant proceeds according to Equation 3:

$\begin{matrix}{{R{OH}} + {9C_{2}H_{4}{O\mspace{14mu}\overset{KOH}{\longrightarrow}\mspace{14mu}{R\left( {{OC}_{2}H_{4}} \right)}_{9}}{OH}}} & {{Eq}.\mspace{14mu}(3)}\end{matrix}$where the fatty alcohol is reacted with ethylene oxide in a 1:9 molarratio yielding a relative mole of reaction product. As shown in Equation3, the reaction product is an ethoxylated fatty alcohol according toFormula (I). As should be appreciated, the degree of ethoxylation mayvary from molecule to molecule by a standardized distribution, wheresome molecules include fewer than the desired number of ethoxy groupsand some molecules include more than the desired number of ethoxygroups.

The ethoxylated alcohol surfactant of the surfactant package may have ahydrophilic-lipophilic balance (HLB) value from 11 to 14. The HLB valueof a molecule is a measure of the degree to which it is hydrophilic orlipophilic. HLB value is calculated by the Griffin Method according toEquation 4:

$\begin{matrix}{{H\; L\; B} = {20*\frac{M_{h}}{M}}} & {{Eq}.\mspace{14mu}(4)}\end{matrix}$where M_(h) is the molecular mass of the hydrophilic portion of themolecule and M is the molecular mass of the whole molecule. HLB valuescalculated using Equation 4 range from 0 to 20 in which a value of 0indicates an absolutely hydrophobic/lipophilic molecule and a value of20 corresponds to an absolutely hydrophilic/lipophobic molecule.Generally, molecules having an HLB less than 10 are lipid soluble,molecules having an HLB greater than 10 are water soluble, and moleculeswith an HLB between 3 and 16 have some surfactant/emulsifyingproperties.

In some embodiments, the ethoxylated alcohol surfactant of thesurfactant package has an HLB value from 11 to 15. In other embodiments,the surfactant package has an HLB value from 12 to 15, from 13 to 15,from 12 to 14, from 13 to 14, from 11 to 12, or from 11 to 13.

The spacer fluids of the present disclosure may further comprise atleast one additive that modifies the rheology of the spacer fluid, thedensity of the spacer fluid, or both. In the context of the presentdisclosure, an additive is a component that is not part of the aqueousexternal phase, the hydrocarbon-based internal phase, or the surfactantpackage. In some embodiments, the additive may comprise a viscosifier tocomport the spacer fluid to the rheology of a particular drilling mud.In other embodiments, this additive may comprise a particulate solidhaving a specific gravity sufficient to increase the density of thespacer fluid without adversely affecting the flowability or otherrheological properties of the spacer fluid.

Examples of additives include, but are not limited to, polysaccharides,polyacrylamides, minerals, defoaming agents, xanthan gum polymer, BaSO₄,Fe₂O₃, FeCO₃, CaCO₃, FeO.TiO₂, bentonite, polyanionic cellulose, orcombinations thereof.

In some embodiments the spacer fluid may comprise from 0.3 pounds to 750pounds of one or more additives per barrel of spacer fluid. In otherembodiments, the spacer fluid may comprise from 10 pounds to 700 pounds,from 15 pounds to 650 pounds, from 20 pounds to 600 pounds, from 25pounds to 500 pounds, from 30 pounds to 400 pounds, from 40 pounds to350 pounds, from 50 pounds to 300 pounds, from 60 pounds to 275 pounds,from 70 pounds to 250 pounds, from 90 pounds to 230 pounds, from 110pounds to 210 pounds, or from 130 pounds to 190 pounds of one or moreadditives per barrel of spacer fluid.

Other embodiments of the present application relate to methods forremoving aqueous based drilling muds from a wellbore. The method maycomprise passing a spacer fluid through the wellbore. The passing spacerfluid may be directed through the annulus and out the outlet of thewellbore. The spacer fluid may then direct the aqueous mud in thewellbore to flow through the annulus and out the outlet of the wellbore.

As previously described, drilling muds can carry formations cuttings outthe outlet of the wellbore. Similarly, spacer fluids can direct ordisplace drilling muds out the outlet of the wellbore. Spacer fluids aremost efficient at displacing drilling muds when the spacer fluid anddrilling mud have similar rheology and the density of the spacer fluidis 5% to 20% greater than the density of the drilling mud.

The spacer fluids of the present disclosure formulated to be compatiblewith certain aqueous drilling muds. In some embodiments, the aqueousdrilling mud that is compatible with spacer fluids of the presentdisclosure comprises from 30 pounds to 351 pounds of water per barrel ofaqueous drilling mud. In other embodiments, the aqueous drilling mudthat is compatible with spacer fluids of the present disclosurecomprises from 225 pounds to 340 pounds, from 245 pounds to 330 pounds,from 265 pounds to 325 pounds, or from 285 pounds to 315 pounds of waterper barrel of aqueous drilling mud.

Other embodiments of the present application relate to a wellbore fluidsystem comprising an aqueous mud and a spacer fluid. The aqueous mud maybe any kind of aqueous drilling mud known or conventionally used inwellbore operations. The spacer fluid may comprise an emulsion, asurfactant package comprising one or more surfactants in the emulsion,and at least one additive. The emulsion may comprise an aqueous externalphase and a hydrocarbon-based internal phase. The surfactant package maycomprise an ethoxylated alcohol surfactant according to formula (I)where R is a hydrocarbyl having from 12 to 14 carbon atoms. Theethoxylated alcohol surfactant of the surfactant package may have an HLBvalue from 11 to 15. The spacer fluid additive or additives may modifythe viscosity of the spacer fluid, the density of the spacer fluid, orboth. In some embodiments of the wellbore fluid system, the density ofthe spacer fluid is 5% to 20% greater than the density of the aqueousmud. In some embodiments of the wellbore fluid system, the differencebetween the yield point of the aqueous mud and the yield point of thespacer fluid may be less than 15 lbs/100 ft². The spacer fluid may havea yield point greater than that of the aqueous mud, a yield point lessthan that of the aqueous mud, or a yield point equal to that of theaqueous mud.

As previously described, spacer fluids have the greatest mud removalefficiency when they have a density from 5% to 20% greater than that ofthe mud the spacer fluid is displacing and similar rheologicalproperties to that of the mud the spacer fluid is displacing. In otherembodiment, a spacer fluid has the greatest removal efficiency when ithas a density from 5% to 15% or from 10% to 15% greater than that of themud the spacer fluid is displacing.

In at least one embodiment, two fluids have similar rheologicalproperties if the difference between their yield points, as measured byAmerican Petroleum Institute Recommended Practice 13B-1, is less than orequal to 15 lbs/100 ft². In other embodiments, two fluids have similarrheological properties if the difference between their yield points, asmeasured by American Petroleum Institute Recommended Practice 13B-1, isless than or equal to 12 lbf/100 ft², less than or equal to 10 lbf/100ft², less than or equal to 5 lbf/100 ft², less than or equal to 4lbf/100 ft², less than or equal to 3 lbf/100 ft², less than or equal to2 lbf/100 ft², less than or equal to 1.5 lbf/100 ft², or less than orequal to 1 lbf/100 ft².

EXAMPLES

Example spacer fluid compositions were prepared to illustrate one ormore additional features of the present disclosure. It should beunderstood that these examples are not intended to limit the scope ofthe disclosure or the appended claims in any manner.

Two example spacer fluids according to embodiments of the presentdisclosure were prepared that included a surfactant package, 51,comprising at least one alcohol ethoxylated surfactant (AES) accordingto the general formula R—(OC₂H₄)₉—OH, where R is a hydrocarbyl havingfrom 12 to 14 carbon atoms. S1 was prepared by ethoxylating a mixture ofisolated naturally occurring C₁₂-C₁₄ fatty acids with nine moles ofethylene oxide. The example spacer fluids were Spacer Fluid 1 and SpacerFluid 2. Spacer Fluid 1 was prepared by adding water, diesel, and tunedspacer E+(a commercially available viscosifier from the HalliburtonCompany) to a multimixer and mixing for 10 minutes. Next, D-Air-3000L (acommercially available defoaming agent from The Halliburton Company) wasadded to the multimixer and mixed for 5 minutes. Then, the surfactantpackage, S1, was added to the multimixer and mixed for 5 minutes.Finally, BaSO₄ was added to the multimixer and mixed for 5 minutes.

Spacer Fluid 2 was prepared by adding to a multimixer amounts of water,safra oil, and tuned spacer E+(a commercially available viscosifier fromthe Halliburton Company) and mixing for 10 minutes. Next, D-Air-3000L (acommercially available defoaming agent from The Halliburton Company) wasadded to the multimixer and mixed for 5 minutes. Then, the surfactantpackage, 51, was added to the multimixer and mixed for 5 minutes.Finally, BaSO₄ was added to the multimixer and mixed for 5 minutes.

As bases for comparing mud removal efficiency of spacer fluids of thepresent disclosure to contemporary spacer fluids, Comparative Fluids A-Ewere made. Comparative Fluid A contained no hydrocarbon-based internalphase and no surfactant. Comparative Fluid B included ahydrocarbon-based internal phase comprising diesel and no surfactant.Comparative Fluid C included a hydrocarbon-based internal phasecomprising diesel and a synthetic AES-type surfactant, C₁₀H₂₁(OC₂H₄)₇OH.Comparative Fluid D included a hydrocarbon-based internal phasecomprising diesel and a surfactant package. The surfactant package ofComparative Fluid D was an AES-type surfactant, namely a mixture ofnaturally derived fatty alcohols ethoxylated with one mole of ethyleneoxide that have the general formula R—(OC₂H₄)—OH, where R is ahydrocarbyl having from 12 to 14 carbon atoms. Comparative Fluid Eincluded a hydrocarbon-based internal phase comprising diesel andLoSurf-259, a commercially available surfactant from The HalliburtonCompany. The compositions of Spacer Fluid 1, Spacer Fluid 2, andComparative Fluids A-E are summarized in Table 1.

TABLE 1 Spacer Spacer Comp. Comp. Comp. Comp. Comp. Fluid 1 Fluid 2Fluid A Fluid B Fluid C Fluid D Fluid E Surfactant Type AES AES NoneNone AES AES LoSurf-259** Carbon atoms in R 12-14 12-14 — — 10 12-14 N/AEthoxylate ratio x 9 9 — — 7 1 N/A Component Concentration (lb/bbl)Water 269.18 269.18 300.31 276.64 269.16 268.96 269.00 Diesel 24.88 0.000.00 25.57 24.88 24.86 24.87 Safra 0.00 24.88 0.00 0.00 0.00 0.00 0.00E+ 11.00 11.00 11.00 11.00 11.00 11.00 11.00 D-Air 0.39 0.39 0.39 0.390.39 0.39 0.39 Surfactant 8.33 8.33 0.00 0.00 8.25 7.54 7.67 BaSO₄ 130.3130.3 132.39 130.48 130.41 131.33 131.17 * AES = an alcohol ethoxylatedsurfactant of the general formula R—(OC₂H₄)_(x)—OH, where R is ahydrocarbyl having the number of carbon atoms specified and x is thespecified molar ratio of ethoxylate to hydrocarbyl in the surfactant.**Losurf-259 is a proprietary surfactant composition commerciallyavailable from Halliburton Company.

A grid test may be performed to assess the mud removal efficiencies ofthe various spacer fluids. As part of the grid test, a grid is coatedwith a mud and then various spacer fluids are tested to determine howefficiently the spacer fluids remove the mud. In preparation for thegrid tests, an example aqueous mud may be prepared for assessing the mudremoval efficiencies of various spacer fluids. An example mud isprepared by adding water and bentonite into a multimixer. These twocomponents are mixed for 20 minutes and then left to rest for 4 to 16hours. Then, XC polymer is added to the multimixer and mixed for 10minutes. Next, potato starch is added to the multimixer and mixed for 5minutes. Then, polyanionic cellulose is added to the multimixer andmixed for 5 minutes. Next, potassium chloride is added to the multimixerand mixed for 5 minutes. Then, sodium hydroxide is added to themultimixer and mixed for 5 minutes. Next, calcium carbonate is added tothe multimixer and mixed for 5 minutes. Finally, BaSO₄ is added to themultimixer and mixed for 5 minutes.

An Example Aqueous Mud was prepared according to the previouslydescribed method having ingredients in the amounts summarized in Table2. Subsequently, grid tests were performed for assessing the mud removalefficiencies of Spacer Fluids 1 and 2 and comparing the mud removalefficiencies of Spacer Fluids 1 and 2 with those of Comparative FluidsA-E.

TABLE 2 Example Aqueous Mud Component Pounds per Barrel (lb/bbl) water311.63 hydrated bentonite 5.00 XC polymer 1.00 potato starch 5.00polyanionic cellulose 1.00 KCl 32.11 NaOH 0.25 CaCO₃ 15.00 BaSO₄ 29.48

As described previously, spacer fluids have the greatest mud removalefficiency when they have a density that is from 5% to 20% greater thanthat of the mud the spacer fluid is displacing. For this reason, SpacerFluids 1-2 and Comparative Fluids A-E were formulated to have a density10% greater than the example mud. Spacer Fluids 1-2 differ fromComparative Fluids A-E in that they comprise different surfactantpackages. The surfactant packages of the fluids of the presentdisclosure, in addition to their role as surfactants, may uniquelymodify the rheology of the fluid in such a way to have similarrheological characteristics to the example mud.

The viscosities of Spacer Fluids 1-2, Comparative Fluids A-E, and theExample Aqueous Mud were measured at shear rates of 10 Hz (600 rpm), 5Hz (300 rpm), 3.33 Hz (200 rpm), 1.67 Hz (100 rpm), 0.1 Hz (6 rpm), and0.05 Hz (3 rpm) using a FANN Model 35 viscometer. Following Equation 1,as provided in the Detailed Description, the plastic viscosity (PV) ofeach fluid was calculated as the difference of the viscosity at 10 Hz(600 rpm) and the viscosity at 5 Hz (300 rpm). Following Equation 2, asprovided in the Detailed Description, the yield point (YP) of each fluidwas calculated as the difference of the viscosity at 5 Hz (300 rpm) andthe plastic viscosity (PV). As described previously, spacer fluids havethe greatest mud removal efficiency when they have similar rheologicalcharacteristics of the mud the spacer fluid is displacing. Individualrheology measurements, PV, YP, and the density of each fluid aredetailed in Table 3.

TABLE 3 Spacer Spacer Comp. Comp. Comp. Comp. Comp. Example PropertyFluid 1 Fluid 2 Fluid A Fluid B Fluid C Fluid D Fluid E Aq. MudViscosity 600 rpm 40 40 66 66 72 46 76 35 (cP) 300 rpm 28 28 45 45 53 2962 26 200 rpm 22 22 38 38 45 24 59 21 100 rpm 16 16 29 29 34 18 53 14  6rpm 6 6 14 14 17 8 30 4  3 rpm 5 5 12 12 15 6 21 2 PV (cP) 12 12 21 2119 17 14 9 YP (lbs/100 ft²) 16 16 24 24 34 12 48 17 Density (pcf) 79.279.2 79.2 79.2 79.2 79.2 79.2 72

As shown in Table 3, Spacer Fluid 1 and 2 as well as ComparativeExamples A-E all had a density 10% greater than that of the ExampleAqueous Mud. However, Spacer Fluid 1 and 2 have YP closer to the ExampleAqueous Mud than any Comparative Example. As explained previously, thiscorrelates to a greater mud removal efficiency for Spacer Fluids 1 and 2as compared to Comparative Examples A-E.

A grid test was performed to measure the mud removal efficiency ofSpacer Fluids 1-2 and Comparative Fluids A-E. In each grid test, a FANNModel 35 viscometer's rotor was fitted with a grid and immersed in theExample Aqueous Mud of Table 3 for 10 minutes and allowed to drip dryfor 2 minutes. The mud coated grid was then weighed to establish astarting weight. The grid was then placed in a viscometer cup preheatedto 140° F. and immersed in the sample spacer fluid. The rotor was thenrotated for 5 minutes at 1.67 Hz (100 rpm), removed from the viscometercup, and allowed to drip dry for 2 minutes. After dripping, the grid wasweighed and the percent difference in weight from the starting weightwas calculated. The percent difference in weight, expressed as anegative number to reflect a decrease of the grid's weight, is alsoknown as the raw mud removal efficiency. This process was repeated atrotation time intervals of 10 minutes, 15 minutes, 20 minutes, and 30minutes to yield mud removal efficiencies for each time interval. Theraw mud removal efficiencies for each of the samples, at all recordedtime intervals are presented in Table 4.

TABLE 4 Raw Mud Removal Efficiency Grid Test Rotation Time (min) Sample5 10 15 20 30 Average Spacer Fluid 1  −23%  −18%  −15%  −23%  −30%  −22%Spacer Fluid 2  −19%  −33%  −48%  −57%  −55%  −42% Comparative Example A−139% −145% −109%  −94%  −88% −115% Comparative Example B −170% −209%−192% −189% −178% −188% Comparative Example C −167% −189% −205% −193%−211% −193% Comparative Example D −344% −403% −384% −389% −396% −383%Comparative Example E −131% −167% −158% −174% −155% −157%

Each raw mud removal efficiency was normalized on a 0-100 scale based onthe maximum and minimum mud removal efficiencies across all fluids. Thenormalized efficiencies are reported in Table 5. The maximum mud removalefficiency, E₁₀₀, was Spacer Fluid 2 at a 15 minute time interval. Theminimum mud removal efficiency, E₀, was Comparative Example C at a 10minute time interval. Each normalized data point in Table 4 wasdetermined by subtracting E₀ from the raw mud removal efficiency,dividing that result by E₁₀₀, and multiplying that result by 100. Onthis normalized scale, 100 represents the greatest mud removalefficiency and 0 represents the least mud removal efficiency. Thenormalization procedure takes into account that some components of thespacer fluids (for example, BaSO₄) stick to the rotor, which can affectthe weight measurements. An average mud removal efficiency wascalculated for each fluid based on the arithmetic average of thenormalized mud removal efficiencies of time intervals 5 minutes, 10minutes, 15 minutes, 20 minutes, and 30 minutes.

TABLE 5 Normalized Mud Removal Efficiency Grid Test Rotation Time (min)Sample 5 10 15 20 30 Average Spacer Fluid 1 98 99 100 98 96 98 SpacerFluid 2 99 95 92 89 90 93 Comparative Example A 68 67 76 80 81 74Comparative Example B 60 50 55 55 58 56 Comparative Example C 61 55 5154 50 54 Comparative Example D 15 0 5 4 2 5 Comparative Example E 70 6163 59 64 63

As shown in Table 5, both of Spacer Fluids 1 and 2 exhibited greaternormalized mud removal efficiency than that of any of the ComparativeExamples A-E. Spacer Fluids 1 and 2 exhibited average normalized mudremoval efficiencies greater than 90. The Comparative Fluid with thegreatest normalized mud removal efficiency, Comparative Example A, had agreatest normalized mud removal efficiency of only 81 (at 30 minutes)and an average mud removal efficiency of 74 over all measured timeintervals.

It should be understood that any two quantitative values assigned to aproperty may constitute a range of that property, and all combinationsof ranges formed from all stated quantitative values of a given propertyare contemplated in this disclosure.

Having described the subject matter of the present disclosure in detailand by reference to specific embodiments, it is noted that the variousdetails described in this disclosure should not be taken to imply thatthese details relate to elements that are essential components of thevarious embodiments described in this disclosure, even in cases where aparticular element is illustrated in each of the drawings that accompanythe present description. Rather, the claims appended hereto should betaken as the sole representation of the breadth of the presentdisclosure and the corresponding scope of the various embodimentsdescribed in this disclosure. Further, it should be apparent to thoseskilled in the art that various modifications and variations can be madeto the described embodiments without departing from the spirit and scopeof the claimed subject matter. Thus it is intended that thespecification cover the modifications and variations of the variousdescribed embodiments provided such modification and variations comewithin the scope of the appended claims and their equivalents.

A first aspect of the disclosure is directed to a spacer fluidcomprising: an emulsion comprising an aqueous external phase and ahydrocarbon-based internal phase; a surfactant package comprising one ormore surfactants, where the surfactant package comprises a surfactanthaving the chemical structure R—(OC₂H₄)₉—OH, where R is a hydrocarbylhaving 12 carbon atoms, and where the surfactant is present in aconcentration of at least 4.25 pounds per barrel of spacer fluid; and atleast one additive that modifies the rheology of the spacer fluid, thedensity of the spacer fluid, or both.

A second aspect of the disclosure includes the first aspect, a spacerfluid comprising: an emulsion comprising an aqueous external phase and ahydrocarbon-based internal phase; a surfactant package comprising one ormore surfactants, where the surfactant package comprises a surfactanthaving the chemical structure R—(OC₂H₄)₉—OH, where R is a hydrocarbylhaving 13 carbon atoms; and at least one additive that modifies therheology of the spacer fluid, the density of the spacer fluid, or both.

A third aspect of the disclosure includes the first or second aspects, Aspacer fluid comprising: an emulsion comprising an aqueous externalphase and a hydrocarbon-based internal phase; a surfactant packagecomprising one or more surfactants, where the surfactant packagecomprises a surfactant having the chemical structure R—(OC₂H₄)₉—OH,where R is a hydrocarbyl having 14 carbon atoms; and at least oneadditive that modifies the rheology of the spacer fluid, the density ofthe spacer fluid, or both.

A fourth aspect of the disclosure includes any of the first throughthird aspects, in which the surfactant package has ahydrophilic-lipophilic balance value from 13 to 15.

A fifth aspect of the disclosure includes any of the first through thirdaspects, in which the spacer fluid has a yield point from 10 lbf/100 ft²to 50 lbf/100 ft² as measured by American Petroleum InstituteRecommended Practice 13B-1.

A sixth aspect of the disclosure includes any of the first through thirdaspects, in which the spacer fluid has a yield point from 10 lbf/100 ft²and 25 lbf/100 ft² as measured by American Petroleum InstituteRecommended Practice 13B-1.

A seventh aspect of the disclosure includes any of the first throughthird aspects, in which the spacer fluid has a density from 62.5 pcf to160 pcf.

An eighth aspect of the disclosure includes any of the first throughthird aspects, in which the spacer fluid has a density from 72.0 pcf to87.5 pcf.

A ninth aspect of the disclosure includes any of the first through thirdaspects, in which the hydrocarbon-based internal phase comprises one ormore of safra oil, diesel, mineral oil, paraffin oil, ben oil, marulaoil, castor oil, palm oil, copra oil, jojoba oil, tung oil, or otheroils naturally derived from plants or animals.

A tenth aspect of the disclosure includes any of the first through thirdaspects, in which the at least one additive comprises one or more ofpolysaccharides, polyacrylamides, minerals, defoaming agents, BaSO₄,CaCO₃, Fe₂O₃, FeCO₃, FeTiO, bentonite, xanthan gum polymer, polyanioniccellulose.

An eleventh aspect of the disclosure includes any of the first throughthird aspects, in which the spacer fluid comprises from 140 pounds to300 pounds of aqueous external phase per barrel of spacer fluid.

A twelfth aspect of the disclosure includes any of the first throughthird aspects, in which the spacer fluid comprises from 0.40 pounds to21 pounds of surfactant package per barrel of spacer fluid.

A thirteenth aspect of the disclosure is directed to A method ofremoving aqueous muds from a wellbore, the method comprising: adding aspacer fluid according to any of the preceding claims to a wellborecomprising an aqueous mud, the spacer fluid comprising:

an emulsion comprising an aqueous external phase and a hydrocarbon-basedinternal phase;

a surfactant package comprising one or more surfactants, where thesurfactant package comprises a surfactant having the chemical structureR—(OC₂H₄)₉—OH, where:

R is a hydrocarbyl having from 12 to 14 carbon atoms and the surfactanthas a hydrophilic-lipophilic balance from 11 to 15; and at least oneadditive that modifies the rheology of the spacer fluid, the density ofthe spacer fluid, or both; passing the spacer fluid through thewellbore, where at least a portion of the aqueous mud exits the wellborethrough a conduit defined by an exterior wall of the tubular and a wallof the wellbore.

A fourteenth aspect of the disclosure includes the thirteenth aspect, inwhich the spacer fluid has a yield point from 10 lbf/100 ft² to 50lbf/100 ft² as measured by American Petroleum Institute RecommendedPractice 13B-1

A fifteenth aspect of the disclosure includes the thirteenth andfourteenth aspects, in which the spacer fluid has a yield point from 10lbf/100 ft² to 25 lbf/100 ft² as measured by American PetroleumInstitute Recommended Practice 13B-1.

A sixteenth aspect of the disclosure includes any of the thirteenththrough fifteenth aspects, in which the hydrocarbon-based internal phasecomprises one or more of safra oil, diesel, mineral oil, paraffin oil,ben oil, marula oil, castor oil, palm oil, copra oil, jojoba oil, tungoil, or other oils naturally derived from plants or animals.

A seventeenth aspect of the disclosure includes any of the thirteenththrough sixteenth aspects, in which the spacer fluid comprises from 140pounds to 300 pounds of aqueous external phase per barrel of spacerfluid.

An eighteenth aspect of the disclosure includes any of the thirteenththrough seventeenth aspects, in which the spacer fluid comprises from0.40 pounds to 21 pounds of surfactant package per barrel of spacerfluid.

A nineteenth aspect of the disclosure includes any of the thirteenththrough eighteenth aspects, in which the at least one additive comprisesone or more of polysaccharides, polyacrylamides, minerals, defoamingagents, BaSO₄, CaCO₃, Fe₂O₃, FeCO₃, FeTiO, bentonite, xanthan gumpolymer, polyanionic cellulose.

A twentieth aspect of the disclosure includes any of the thirteenththrough nineteenth aspects, in which the aqueous mud comprises from 30pounds to 351 pounds of water per barrel of aqueous mud.

A twenty-first aspect of the disclosure includes any of the thirteenththrough twentieth aspects, in which the aqueous mud comprises from 4pounds to 420 pounds of alkali metal salt or alkali earth metal salt perbarrel of aqueous mud.

A twenty-second aspect of the disclosure is directed to a wellbore fluidsystem comprising: an aqueous mud in a wellbore; and a spacer fluid incontact with the aqueous mud in the wellbore, the spacer fluidcomprising: an emulsion comprising an aqueous external phase and ahydrocarbon-based internal phase; a surfactant package comprising one ormore surfactants, where the surfactant package comprises a surfactanthaving the chemical structure R—(OC₂H₄)₉—OH, where: R is a hydrocarbylhaving from 12 to 14 carbon atoms and the surfactant has ahydrophilic-lipophilic balance from 11 to 15; and at least one additivethat modifies the rheology of the spacer fluid, the density of thespacer fluid, or both; in which: the density of the spacer fluid, asmeasured by American Petroleum Institute Recommended Practice 13B-1, is5% to 20% greater than the density of the aqueous mud as measured byAmerican Petroleum Institute Recommended Practice 13B-1; and thedifference between the yield point of the aqueous mud, as measured byAmerican Petroleum Institute Recommended Practice 13B-1, and the yieldpoint of the spacer fluid, as measured by American Petroleum InstituteRecommended Practice 13B-1, is less than or equal to 15 lbf/100 ft².

A twenty-third aspect of the disclosure includes the twenty-secondaspect, in which the density of the spacer fluid is 10% to 20% greaterthan the density of the aqueous mud.

A twenty-fourth aspect of the disclosure includes the twenty-second andtwenty-third aspects, in which the density of the spacer fluid is 10% to15% greater than the density of the aqueous mud.

A twenty-fifth aspect of the disclosure includes any of thetwenty-second aspect, in which the difference of the yield point of theaqueous mud and the yield point of the spacer fluid is less than orequal to 10 lbf/100 ft².

A twenty-sixth aspect of the disclosure includes any of thetwenty-second through twenty-fifth aspects, in which the difference ofthe yield point of the aqueous mud and the yield point of the spacerfluid is less than or equal to 5 lbf/100 ft².

What is claimed is:
 1. A wellbore fluid system comprising: an aqueousmud in a wellbore; and a spacer fluid in contact with the aqueous mud inthe wellbore, the spacer fluid comprising: an emulsion comprising anaqueous external phase and a hydrocarbon-based internal phase; asurfactant package comprising: one or more surfactants having thechemical structure R(OC₂H₄)₉—OH, where R is a hydrocarbyl having from 12to 14 carbon atoms and the surfactant has a hydrophilic-lipophilicbalance from 11 to 15; and at least one additive that modifies therheology of the spacer fluid, the density of the spacer fluid, or both;in which: the density of the spacer fluid, as measured by AmericanPetroleum Institute Recommended Practice 13B-1, is 5% to 20% greaterthan the density of the aqueous mud as measured by American PetroleumInstitute Recommended Practice 13B-1; and the difference between theyield point of the aqueous mud, as measured by American PetroleumInstitute Recommended Practice 13B-1, and the yield point of the spacerfluid, as measured by American Petroleum Institute Recommended Practice13B-1, is less than or equal to 15 lbf/100 ft².
 2. The wellbore fluidsystem of claim 1, in which the density of the spacer fluid is 10% to20% greater than the density of the aqueous mud.
 3. The wellbore fluidsystem of claim 1, in which the density of the spacer fluid is 10% to15% greater than the density of the aqueous mud.
 4. The wellbore fluidsystem of claim 1, in which the difference of the yield point of theaqueous mud and the yield point of the spacer fluid is less than orequal to 10 lbf/100 ft².
 5. The wellbore fluid system of claim 1, inwhich the difference of the yield point of the aqueous mud and the yieldpoint of the spacer fluid is less than or equal to 5 lbf/100 ft².
 6. Thewellbore fluid system of claim 1, in which the surfactant package has ahydrophilic-lipophilic balance value from 13 to
 15. 7. The wellborefluid system of claim 1, in which the spacer fluid has a yield pointfrom 10 lbf/100 ft² to 50 lbf/100 ft² as measured by American PetroleumInstitute Recommended Practice 13B-1.
 8. The wellbore fluid system ofclaim 1, in which the spacer fluid has a yield point from 10 lbf/100 ft²and 25 lbf/100 ft² as measured by American Petroleum InstituteRecommended Practice 13B-1.
 9. The wellbore fluid system of claim 1, inwhich the spacer fluid has a density from 62.5 pcf to 160 pcf.
 10. Thewellbore fluid system of claim 1, in which the spacer fluid has adensity from 72.0 pcf to 87.5 pcf.
 11. The wellbore fluid system ofclaim 1, in which the hydrocarbon-based internal phase comprises one ormore of safra oil, diesel, mineral oil, paraffin oil, ben oil, marulaoil, castor oil, palm oil, copra oil, jojoba oil, tung oil, or otheroils naturally derived from plants or animals.
 12. The wellbore fluidsystem of claim 1, in which the spacer fluid comprises from 140 poundsto 300 pounds of aqueous external phase per barrel of spacer fluid. 13.The wellbore fluid system of claim 1, in which the spacer fluidcomprises from 0.40 pounds to 21 pounds of surfactant package per barrelof spacer fluid.
 14. The wellbore fluid system of claim 1, in which theat least one additive comprises one or more of polysaccharides,polyacrylamides, minerals, defoaming agents, BaSO₄, CaCO₃, Fe₂O₃, FeCO₃,FeTiO, bentonite, xanthan gum polymer, polyanionic cellulose.